The effects of an acidic environment on selected geophagic clayey samples and its impact on the bioavailability of certain elements

Geophagia, the deliberate ingestion of non-food lithospheric substances, is a major form of pica in most African cultures. A common pica substance sold in the central business district of Johannesburg, Gauteng Province, South Africa, is a yellowish-brown clay soil. Women of reproductive age usually ingest this clay. Alluring flavour, alleviation of nausea during pregnancy, and absorption of toxins in the gastrointestinal tract are some of the reasons why people engage in geophagia. There are claims that geophagia helps to replenish mineral nutrients in malnourished individuals. The study of the acid extractable mineral contents of some selected geophagic clays was to provide information on the absorbable minerals in the gastrointestinal tract. Six representative clay samples being sold in identified informal markets were investigated using scientific techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and atomic absorption spectrometry (AAS). Results showed that the clay soil was very dry with an average moisture content of 0.31 ± 0.01%. The average concentrations of the minerals in the acid extract were aluminium (1.55 mg/l), iron (1.84 mg/l), copper (0.19 mg/l), lead (0.19 mg/l), zinc (0.30 mg/l), cobalt (0.07 mg/l), and nickel (0.04 mg/l). Nickel was detected in neither the water extracts nor acid extracts of sample GNG1. Sample GNG2 also did not have detectable cobalt in either of the two extracts. Based on the percentage extractable data, aluminium was the most extractable metal. Based on the recommended daily allowance, the clayey soil samples liberated high amounts of nickel and lead, which could pose a danger to the body.